I don't really understand why I would need scientists instead of taxmen. Scientists don't speed up build time, engineer's do. Their only used for increasing science for tech research, correct?. So if I have the science slider at 50%, and so many scientists to equal another 50%, then I would have a total of 100%, correct?. It would be much better building factories and plants that increase shield output, yes?.
I run at 100% science, except when a tech has one turn left, then I pull the slider back to increase treasury money. Making sure not to pull it back to far and increase the research time.
It is not common to run at 100%, except at the very start or late in the game. Most will run at least something on the lux slider. Once you move above Regent you will surely have to running more as you have fewer contented citizens.
A more reasonable rate would be 70-80% and slide up or down fromm time to time to either get it done sooner or save.
Scientist give 3 net beakers, taxman give 2 net gold. 3 is more than 2. It is true that could do a lot of switching to gain the max benefit, but that is more work than even I do most of the time (outside of an SG).
The scientis will let you drop the slider down farther or sooner near the break through and give you back gold in that manner. Taxmen I do not run, unless I am not researching or I am trying to get through one turn with no loss and also not drop research down.
Factories are another whole issue and I have already told my take on them. They are so late in the game as to not be important to me. I am in mop up mode at that stage, even if it looks like I am in trouble. I have reached critical mass.
I tend to make only a few factories, even on a huge Sid conquest game. I just do not need more prodution at that phase. I am gaining more and more leaders making more and better armies. That means more and higher kill ratios. I just need to make enough units to fill my armies as I get them.
Maybe 4 cities with factory. Maybe 2-4 other cities making troops at a slower rate. I usually no longer need more artillery as I have rails and will capture bombardment units as well.
Should I need a unit someplace else, I can rush it. If you want to make more factories, fine. I would advise picking only places that can really use them. Not those 10 net shields cities.
What is the value of making a factory and cutting my tank from 10 turns to 7 and taking 24 turns to build it? I have to pay for it and clean up after it for a tank I do not really even need.
Remember I do not care about time or speed. I care about not letting them even feel my boot pressure reduced slightly off their neck.